A turbine powered generator, or turbo-generator, for energy conversion includes a frame structure that is typically installed over a concrete foundation that provides the needed structural support for the generator. There are usually one or more feet along portions of the frame that help transfer the load of the generator frame to the foundation. The weight supported by the generator feet is typically transmitted to the foundation through a shim pack, seating plate and grouting. Varying the shim pack thickness permits alignment between the generator and the turbine during erection and maintenance. The seating plate, grouted to the foundation during erection, provides a solid base of support for the generator. Frame feet that may extend the full length of the frame are typically loaded uniformly, using shim packs whose uniform thickness is modified only to obtain final alignment of the generator to the turbine. Thus, the stator core weight and electrical load are carried by the central portion of the generator while the frame ends support the rotor in the bearings.
To minimize the generator shaft bearing span and to increase stiffness, the rotor bearings can be supported by respective brackets on each end of the frame structure, instead of being supported by external bearing pedestals. This arrangement of the bearings means that the frame feet at the ends of the generator should provide solid support for the rotor shaft and bearings. In the past, electro-mechanical strain gauges have been used on frame ribs, or gussets, to measure load distribution on each foot and to optimize the foot's position for dynamic bearing loads. A load distribution pattern based on frame deflection is used for proper frame foot loading. In particular, one or more electro-mechanical strain gauges have been used on one or more gussets that are located near the corners of the frame structure; it is these vertical support gussets that bear the frame weight at the corners.
The use of electro-mechanical strain gauges in the manner described above introduces some reliability and operational constraints. First, the standard electro-mechanical strain gauges are typically bonded to the gusset substrate via a hydroscopic cement, that can sometimes fail. Even when care is taken to coat the strain gauges with a sealant to keep moisture out, the bond life of the cement can be as brief as 12-18 months. Thus, generators that have been frame foot loaded in the past will need to have the old strain gauges removed and new strain gauges installed for future frame foot loading.
Also, the installation of standard electro-mechanical strain gauges is time consuming even for an experienced technician. A standard strain gauge installation by experienced field personnel is estimated to be about 1 hour for each strain gauge. Thus, by way of example, a typical installation for a four-pole generator may include up to 64 strain gauges to properly instrument the gussets and can therefore require significant installation time.
Also, by design, each standard strain gauge typically requires 3 wires for measurement. For a four-pole generator, as many as 256 wires may need to be routed from the generator to the strain gauge analog connectors. These connections also introduce a large amount of time needed for making final measurements.
Thus, there remains the need to perform frame foot loading measurements for a power generator in a fast, efficient and accurate manner and in a way that ensures reliable results for long periods of time.